When the price of the underlying equity, index or commodity equals the strike price of the option.

The notification to the seller of an option by the clearing corporation that the buyer of the option is enforcing the terms of the option's contract.

An option is at-the-money if the strike price of the option is equal to the market price of the underlying security. For example, if a company's stock is trading at $68, then the company's $68 option is at-the-money.